Zinc electroplating solution and methods



United States Patent 3,020,218 ZINC ELECTROPLATING SOLUTION AND METHODS Aloysius G. Catferty, Venice, Califi, assignor to Western glecktric Company, Incorporated, a corporation of New or No Drawing. Filed July 28, 1960, Ser. No. 45,797 4 Claims. (Cl. 204-55) The present invention relates generally to zinc electroplating solutions and methods, and more particularly zinc electroplating solutions and methods utilizing nontoxic ingredients.

In most galvanizing or zinc plating applications, cyanide-containing electroplating solutions are used, which solutions are highly toxic and present considerable problems in disposing of the cyanide wastes.

The primary object of the present invention is to prm vide new and improved zinc electroplating solutions and methods, which do not utilize cyanide or other solutions involving toxic ingredients.

With these and other objects in view, a zinc plating solution embodying certain features of the invention consists essentially of an aqueous solution of zinc acetate, between approximately 30 and 90 grams per liter; citric acid, between approximately 1.5 and 3 times the gramsper-liter concentration of the zinc acetate; and a sufiicient quantity of an alkaline pH-modifying substance to adjust the pH to a value within the range of about 4 to 5.5.

A method of electroplating, in accordance with the principles of the invention, may include the step of electroly'zing a solution as described in the preceding paragraph at a current density within the range of about 25 to 50 amperes per square foot. Preferably, the solution is heated to a temperature within the range of about 120 to 150 F. during the electroplating operation.

Example While electroplating solutions according to the invention may be formulated within the general ranges indicated in the preceding paragraphs, one specific preferred example is as follows:

Zinc acetate-6O grams per liter;

Citric acid-150 grams per liter;

Sodium hydroxide-Sufficient to adjust the pH to a value Temperature-140 F.; and

Current density-40 amperes per square foot.

Plating solutions in accordance with the invention may be operated over a wide range of temperatures; however, it is preferred to heat the solution somewhat, with best results being obtained within the range of about 120 to 150 F.

I Althougt the current density may be varied considerably as is customary for ditferent applications, a current density within the range of about 25 to 50 amperes per square foot produces excellent results in most instances.

Electrolytes according to the invention have been found to operate most satisfactorily with a pH between about 4 and 5.5. The acidity is adjusted with a suitable alkaline pH-modifying substance, preferably sodium hydroxide, for optimum results to a value between about 4.5 and 5.

The mechanics of the plating process are generally conventional, whereby electroplating solutions as described above may be used to deposit zinc on a variety of objects to be galvanized, such as ferrous and cuprif erous piece parts. -As is customary, the object to be plated is made cathodic and is either dipped or is moved continuously through the electroplating bath. The anodes may be constructed either of zinc or of an inert material, such as carbon. Several desirable solution properties are obtained with this electrolyte, especially good throw ing power which is attributed to the formation of a complexion between the zinc and citrate ions.

While various specific examples and embodiments of the invention have been described in detail hereinabove, it will be obvious that various modifications may be made from the specific details described without departing from the spirit and scope of the invention.

What is claimed is:

1. A zinc electroplating solution consisting essentially of an aqueous solution of zinc acetate, between approximately 30 and grams per liter; citric acid, between approximately 1.5 and 3 times the grams-per-liter concentration of the zinc acetate; and a sufiicient quantity of an alkaline pH-modifying substance to adjust the pH to a value within the range of about 4 to 5 .5.

2. The method of electroplating, which comprises the step of electrolyzing the solution recited in claim 1 at a current density within the range of about 25 to 50 amperes per square foot.

3. A zinc electroplating solution consisting essentially of an aqueous solution of zinc acetate, approximately 60 grams per liter; citric acid, approximately 150 grams per liter; and a sufiicient quantity of sodium hydroxide to adjust the pH to a value between about 4.5 and 5.

4. The method of electroplating, which comprises the step of electrolyzing the solution recited in claim 3 at a current density of about 25 to 50 amperes per square foot while heated to a temperature within the range of about to F.

References Cited in the file of this patent UNITED STATES PATENTS 2,421,265 Hogaboom May 27, 1947 

1. A ZINC ELECTROPLATING SOLUTION CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF ZINC ACETATE, BETWEEN APPROXIMATELY 30 AND 90 GRAMS PER LITER; CITRIC ACID, BETWEEN APPROMIXIMATELY 1.5 AND 3 TIMES THE GRAMS-PER-LITER CONCENTRATION OF THE ZINC ACETATE; AND A SUFFICIENT QUANTITY OF AN ALKALINE PH-MODIFYING SUBSTANCE TO ADJUST THE PH TO A VALUE WITHIN THE RANGE OF ABOUT 4 TO 5.5. 